1. Field of the Invention
The present invention relates to method and apparatus for accessing data tracks on an optical disk.
2. Description of the Related Art
In general, an optical disk is a circular plate. The diameter of the inner-most track of the optical disk is about 50 mm, and the diameter of the outer-most track is about 116 mm.
When an optical disk with such dimensions is reproduced, the disk is rotated in a constant angular velocity (CAV) mode as shown in FIG. 1, so that the reproduction speed, that is, the linear velocity of a track is increased as the reproduction position moves radially outward. According to the above characteristics, when an optical pickup is moved radially by a sled motor to process a long jump from a current reproduction position to a new desired position, the reproduction speed will have to be increased or decreased at the target track. Signals reproduced from the target track can be restored into original data only after a data reading clock is synchronized with the signals reproduced at the new speed. This operation is explained in more detail below.
The frequency of reproduced signals changes when an optical pickup moves to a target track, and a phase lock loop (PLL) tries to synchronize an internal data reading clock, in frequency and phase, with the signals reproduced at the target track.
During the synchronizing process, if a predetermined number of sync signals are detected from the high frequency signals (referred as xe2x80x98RF signalsxe2x80x99 hereinafter) read out by an optical pickup within a specific time window, a good frame sync (GFS) signal is generated. Because the GFS signal means successful synchronization, the reproduced signals can be processed and restored into original data using the synchronized data reading clock just after the GFS signal is generated.
However, because the above-explained data track accessing method gradually changes the data reading clock, synchronized with reproduced signals from the current frequency, to a different frequency synchronized with signals reproduced from the target track, generation of the GFS signal is delayed. And, when the optical pickup moves a long distance, the difference in reproduction speed between a current track and a desired track is too large to perform synchronization gradually. As a result, synchronization of the data reading clock with signals reproduced from the desired or target location occasionally fails, and this failure in synchronization causes a spindle motor to diverge.
The apparatus and method for accessing data tracks of an optical disk adjust a data reading clock, used in converting reproduced signals into digital data, before the movement of an optical pickup to a target location is completed. When a track jump request is received, the current rotation speed is measured, and using a linear function, a controller calculates the reproduction speed at the target location based on the current rotation speed and the target location. The controller then adjusts the data reading clock based on the calculated reproduction speed.
Because the data reading clock is adjusted prior to reproduction at the target location, signals reproduced at the target location can be readily converted into digital data. This significantly reduces access time and improves the stability of the reproduction operation.